Document EP-A-0547922, among many others, makes known such a machine for printing flat objects (envelopes in particular) of various thicknesses successively transported the length of a table by means of a feed mechanism and printed by means of a printing mechanism, the feed mechanism comprising at least two rollers, at least one roller of which is motorized, between which the objects pass, the printing mechanism comprising a turning printing drum and a motorized counter-printing roller.
The current machines printing the cancellation or prepayment marks with the aid of a rotative drum use one motor to drive the envelopes and another to drive the printing drum. The movement of the drum is described precisely in Document WO-A-96/26502. The drive motor of the printing drum performs an abrupt acceleration movement to permit the drum to meet the letter in perfect synchronization. Further, to permit the handling of thick envelopes, the drive motor of the printing drum must shift the counter-printing roller. As this last is firmly pressed against the drum, the abrupt movement performed by the drive motor is very important.
On the other hand, stepping motors are employed more and more for the printing drum motorization. While these show great advantages, they are nevertheless sensitive to abrupt changes in load.